This invention relates to a pinch valve which comprises a flow control member in the form of a flexible tube member as a portion of a fluid line and arranged for being connected to the fluid line by means of two adapter pieces. A pinch valve of the kind to which the present invention relates is more generally referred to by the introductory portion of claim 1.
The European Patent Publication EP 0 097 288 B1 discloses a pinch valve of the kind in which a flexible tube member forms a portion of a fluid line. The fluid line is arranged for feeding an air containing tooth cleaning powder to a nozzle of a dental handpiece of a prophylactic apparatus for cleaning teeth in combination with a flow of water as also supplied to said nozzle for being sprayed in common with the particles of the cleaning powder against a tooth surface under treatment. The known pinch valve is structured with a cylindrical valve chamber through which the flexible tube member is passed. A pneumatically moveable piston is arranged in the valve chamber for being moved against the bias force of a spring. The piston when moved pneumatically under a predetermined actuating pressure acts on the flexible tube member When the flexible tube member is fully pinched by the piston so that no air containing tooth cleaning powder particles will anymore reach the nozzle of the handpiece. When otherwise the actuating pressure on the piston has been stopped the piston will be retracted by the force of the bias spring and a free passageway for the cleaning powder will again be obtained. For avoiding any excessive stress of the flexible material of the flexible tube member an alternative embodiment of the known pinch valve is provided with a piston which is as well pneumatically moveable but which houses a separate pressure member which is influenced by a spring force in such a manner that when the piston has reached a stop position with respect to the valve chamber under a predetermined actuating pressure the bias spring will then force the pressure member into contact with the flexible tube member for its pinching so that with a flow blocking of the cleaning powder the cleaning of the tooth surface will then be interrupted.
The British Patent GB 2, 147, 394 A discloses a pinch valve in which a portion of a flexible fluid line is passed through a cylindrical valve chamber for being actuated by a pneumatically moveable piston. The valve chamber through which a fluid line is passed comprises a lining structured as a sleeve of a highly flexible material of a substantial thickness such as a porous rubber material or a porous plastic material. The sleeve serves the purpose of avoiding an excessive stress of the fluid line when it is pinched by the piston also for blocking the flow of air containing tooth cleaning powder particles to a nozzle of a dental handpiece of a prophylactic apparatus.
The German Patent Publication DE-AS 1 097, 778 discloses a pinch valve in which a flexible tube member forms a flow control member as a portion of a fluid line. The flexible tube member comprises at least two layers of different flexible properties which two layers are in contact with each other as being either relatively moveable or fixedly interconnected. The flexible tube member is inserted into a valve chamber in an exchangeable manner for being actuated by an actuator which is moveable by means of a spindle drive. The outer layer of the flexible tube member is arranged for supporting the inner layer so that for such supporting purposes the outer layer is structured as a molded body of a respectively thick rubber material in comparison with the inner layer. The inner layer comprises a relatively thin foil or film made of a material which is chosen under consideration of the flow characteristics of the fluid which is to be controlled by the pinch valve when being transported through the fluid line. The inner layer of the flexible tube member therefore specifically comprises a plastic material of a much higher wear resistance and of a much better coefficient of friction than the rubber material of the outer layer.
An object of the present invention is to provide a pinch valve of the kind as above described which will allow a simple exchange of the flexible tube member with an easily manufacturable structure of the valve. The pinch valve should also be structured such as to allow a very sensitive variable flow control of a fluid which is transported through the fluid line whereby the flow should be continuously controllable between a maximum and a minimum value.
In accordance with a present invention a pinch valve of the general kind as referred to is provided with a flexible tube member which is arranged on a separate insert member. This separate insert member is made of a rigid material for supporting the flexible tube member and comprises a sealed connection with the two adapter pieces of the fluid line in common with the flexible tube member. The insert member is inserted into a valve housing of the pinch valve in such a manner that the actuator may directly contact the flexible tube member for pinching the same when actuated.
By arranging the flexible tube member on a separate rigid insert member less wear resistance of the flexible tube member will exist. The flexible tube member may therefore be pinched many more times until it gets broken in comparison with the structures of the known pinch valves so that constant control characteristics may be obtained over an extended period of time until an exchange of the flexible tube member becomes necessary. By providing the specific arrangement of the flexible tube member on a rigid insert member this will also allow the provision of a one-way component of the pinch valve for an easy exchange of which there would be provided a suitable ejection opening in the valve chamber of the valve housing through which on the other side such a insert member is insertable into the valve chamber.
Other objects, features and advantages of the present invention will become apparent from reading the following description of a preferred embodiment of a pinch valve according to the present invention.